Salesforce JavaScript Developer Practice Exam

What type of object is always returned when using async in JavaScript?

1. Null

2. String

3. Promise

4. Map

The correct answer is: Promise

When using async in JavaScript, a Promise is always returned. The async keyword is a way to define a function that will always return a Promise, regardless of whether the typical return value from the function is an explicit Promise or a value directly. If a value is returned from the function, JavaScript automatically wraps it in a Promise that resolves with that value. This behavior is foundational to how asynchronous operations work in JavaScript, allowing for a consistent interface when handling asynchronous code. Even if you don't explicitly return a Promise, wrapping a non-Promise return value ensures that callers of the async function can use `.then()` and `.catch()` to handle the result or any potential errors. This leads to more predictable and manageable asynchronous code. In contrast, other options like Null, String, or Map do not have the same guarantees. Null would not be useful for handling async operations, Strings are simply data types and not related to the async behavior itself, and Map is a collection type that doesn't have any relationship to the return value of an async function. Thus, understanding that the async function guarantees a Promise return type is crucial for working effectively with asynchronous code in JavaScript.